The Kelly Drive Bushing acts as an adapter that serves to connect the rotary table to the Kelly. The Kelly bushing has an inside diameter profile that matches that of the Kelly, usually square or hexagonal. It is connected to the rotary table by four large steel pins that fit into mating holes in the rotary table. The rotary motion from the rotary table is transmitted to the bushing through the pins, and then to the kelly itself through the square or hexagonal flat surfaces between the Kelly and the Kelly drive bushing. The Kelly then turns the entire drillstring because it is screwed into the top of the drillstring itself.
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